Of his fifteen books on Josephus and 138 articles on Josephus and Judaism, I would like to quote what this Josephian scholar says about the Testimonium Flavaianum taken from "Josephus (CE 37-c.100)," in William Harbury et al., ed., The Cambridge History of Judaism vol. 3 (1999) pp. 911 - 912.

“We may remark here on the passage in Josephus which has occasioned by far more comment than any other, the so-called Testimonium Flavianum (Ant. XVIII. 63 - 4) concerning Jesus. The passage appears in all our manuscripts; but a considerable number of Christian writers - Pseudo-Justin and Theophilus in the second century, Minucius Felix, Irenaeus, Clement of Alexandria, Julius Africanus, Tertullian, Hippolytus and Orgen in the third century, and Methodius and Pseudo-Eustathius in the early fourth century - who knew Jeosphus and cited from his works do not refer to this passage, though one would imagine that it would be the first passage that a Christian apologist would cite. In particular, Origen (Contra Celsum 1.47 and Commentary on Matthew 10.17), who certainly knew Book 18 of the Antiquities and cites five passages from it, explicitly states that Josephus did not believe in Jesus as Christ. The first to cite the Testimonium is Eusebius (c. 324); and even after him, we may note, there are eleven Christian writers who cite Josephus but not the Testimonium. In fact, it is not until Jerome in the early fifth century that we have another reference o it.

The principal internal argument against the genuineness of the Testimonium is that it says that Jesus was the Christ, whereas Josephus, as a loyal Pharisaic Jew, could hardly have written this. To be sure, there was several claimants to the status of Messiah in this era, and those who followed them were not read out of the Jewish fold; but in view of the fact that Josephus nowhere else uses the word Christos (except in referring to James, the brother of Jesus, Ant. XX.200) and that he repeatedly suppresses the Messianic aspects of the revolt against Rome because of the association of the Messiah with political revolt and independence, it would seem hard to believe that he would openly call Jesus a Messiah and speak of him in awe. The fact that Jerome (De viris illustrious 13) read that ’he was believed to be the Christ (credebatur esseChristus) would suggest that his text differed from ours. Another objection to the authenticity of the passage is that it breaks the continuity of the narrative, which tells of a series of riots. Those, such as Eisler, who regard the passage as interpolated, suggest that the original spoke of the Christian movement as a riot.

Pines (An Arabic Version of the Testimonium Flavianum and Its Implications (Jeruslame 1971))has created a considerable stir by bringing to the scholarly world’s attention two hitherto almost completely neglected works containing the Testimonium, one a tenth-century history of the world in Arabic by a Christian named Agapius and the other a twelfth-century chronicle in Syriac by Michael the Syrian. There are a number of differences between Agapuius and our Testimonium, notably in the omission of the statement ‘if one ought to call him a man’ and of Jesus’ miracles and of the role of the Jewish leaders in accusing Jesus, and, above all, in the assertion that Jesus was perhaps the Messiah (‘was thought to be’ in Michael). Since Agapius declares that ‘This is what is said by Josephus and his companions’ and indeed includes a number of other details not found in Josephus, we may conjecture that he used other sources as well. Inasmuch as there are changes in the order of the statements of the Testimonium in Agapius and Michael, we are apparently dealing not with a translation but with a paraphrase.”

So, by the account given by Louis Feldman, Christians are not above forgery and lies to give credence to Christianity!